I have searched so many sites and have managed to duplicate the fire truck and ambulance siren, but does anyone have the schematics for the yelp, and the hail 1 and hail 2 for the US police sirens? With 2 lm555 timers in a sweeping output frequency schematic I was able to emulate a realistic sounding slow siren and up and down ambulance but I cannot get it to do the fast smooth rotating police sound. The only yelp schematic I have found uses unijunction transistors and I cannot find those anywhere.

I have another sheet with a very similar schematic, that has a list of substitutes I tried. To be honest I thought that was the one I used in the original forum long long ago (this was a recycled picture).